1. Field of the Invention
The invention relates to novel methods of preparing a liquid sample, and to novel apparatuses for preparing a liquid sample. The invention further relates to novel methods and apparatuses for performing an analytical measurement. The invention has particular applicability in liquid-sample preparation for analytical techniques such as liquid chromatography, for example, ion chromatography, and more specifically to the detection of impurities in a liquid sample, such as in liquid chemicals used in the semiconductor-manufacturing industry.
2. Description of the Related Art
In the semiconductor-manufacturing industry, ultra-high-purity chemicals such as hydrogen peroxide (H2O2), hydrochloric acid (HCl), nitric acid (HNO3), hydrofluoric acid (HF), ammonium hydroxide (NH4OH) and deionized water, among many others, are employed in processes such as wafer-cleaning and/or etching. It is imperative that the impurity levels in such chemicals be as low as possible, since yields of the semiconductor devices being formed can be adversely affected by the impurities. With current device geometries, the presence of impurities on the parts-per-trillion (ppt) level can be problematic. In light of the foregoing, the analytical techniques used by chemical suppliers and users of the chemicals, such as semiconductor manufacturers, are becoming more critical.
During analysis of the liquid chemical, impurities can be added to the sample by virtue of the analysis technique itself, for example, in manually loading the liquid chemical into the analytical instrument. To prevent such external contamination of the sample, pneumatic loading methods have been developed and are currently employed for liquid-sample introduction into the analytical instrument. An apparatus for performing such function is commercially available, for example, from Dionex Corporation, Sunnyvale, Calif. L. Vanatta, J. Chromatogr. A 739 (1996), pp. 199-205, describes a method and apparatus for pneumatically loading a liquid sample into a liquid chromatograph.
Use of a pressurizable vessel for pneumatically transporting the liquid sample from a sample holder to the analytical instrument inlet has been considered a substantially contamination-free technique for sample loading. In this method, the liquid sample is typically contained in an open sample holder, which is manually placed inside a pressurizable vessel. This placement is accomplished by removing the lid of the vessel, placing the liquid sample on a stage at the bottom of the vessel, and replacing and securing the lid. The vessel includes a gas inlet connected to an inert-gas source, and a liquid-sample conduit extending from the sample holder (below the liquid surface) through the vessel lid. The inert gas is introduced into the vessel, thereby raising the pressure in the vessel and thus the pressure over the surface of the liquid sample. With sufficient pressure, the liquid sample is forced to flow through the sample conduit and into the analytical-instrument sample-loading port.
While the above described method and apparatus can perform adequately for the measurement of certain analytes, particular analytes are problematic in obtaining accurate measurements. In particular, it has been found that analytes that are also present in the atmosphere in which the measurement is being conducted and that have a high solubility in the liquid chemical being measured give rise to inaccurate measurements. This problem is aggravated as the analyte solubility increases with pressurization of the vessel during sample loading.
For example, ammonia is typically present in the laboratory atmosphere in which the sample preparation and measurement are conducted. Ammonia is very soluble in water and, during pressurization of the vessel with the inert gas, the ammonia solubility increases even further. As a result, the ammonia is driven into solution and forms ammonium ions in the liquid sample. In the case where ammonium is the analyte of interest, an accurate measurement of the liquid sample would not be possible because of this artificial increase in ammonium content. The practical effect of this situation is that all blanks, standards, and samples to be measured become contaminated, resulting in inaccurate quantification of impurity levels. Other examples of materials that may pose similar problems are organic solvents, such as alcohols and acetone, which are commonly used in analytical laboratories.
To overcome or conspicuously ameliorate the aforementioned problems associated with the related art, it is an object of the present invention to provide methods of preparing a liquid sample.
It is a further object of the invention to provide methods of performing an analytical measurement.
It is a further object of the invention to provide apparatuses for preparing a liquid sample which apparatuses can be used to practice the inventive methods.
It is a further object of the invention to provide apparatuses for performing an analytical measurement. Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended hereto.
According to a first aspect of the invention, a method of preparing a liquid sample is provided. The method comprises: providing a pressurizable vessel that contains a liquid sample in a container, and a sample tube extending from beneath the surface of the liquid sample to a point outside of the vessel; introducing a purge gas into the vessel through a purge-gas inlet conduit, and simultaneously removing the gas atmosphere in the vessel through a purge-gas outlet conduit, thereby displacing the atmosphere in the pressurizable vessel; and pressurizing the vessel with the purge gas to transfer a portion of the liquid sample from the container through the sample tube.
According to a further aspect of the invention, provided is a method of performing an analytical measurement. The method comprises: providing a pressurizable vessel that contains a liquid sample in a container, and a sample tube extending from beneath the surface of the liquid sample to an analytical instrument; introducing a purge gas into the vessel through a purge-gas inlet conduit, and simultaneously removing the gas atmosphere in the vessel through a purge-gas outlet conduit, thereby displacing the atmosphere in the pressurizable vessel; pressurizing the vessel with the purge gas to transfer a portion of the liquid sample from the container through the sample tube; and introducing the liquid sample into the analytical instrument.
According to a further aspect of the invention, provided is an apparatus for preparing a liquid sample. The apparatus comprises: a pressurizable vessel comprising one or more walls, and a plurality of apertures in the walls, the apertures comprising one or more purge-gas inlet apertures and one or more purge-gas outlet apertures; one or more purge-gas inlet conduits connected to the pressurizable vessel in fluid communication with the purge-gas inlet apertures, for introducing a purge gas through the purge-gas inlet apertures; a liquid-sample container for holding a liquid sample inside the pressurizable vessel; a sample tube extending from beneath the surface of the liquid sample in the container to a point outside of the pressurizable vessel for pneumatically transferring the liquid sample from the liquid-sample container to the point outside of the pressurizable vessel.
According to a further aspect of the invention, provided is an apparatus for performing an analytical measurement. The apparatus comprises: an analytical instrument; a pressurizable vessel comprising one or more walls, and a plurality of apertures in the walls, the apertures comprising one or more purge-gas inlet apertures and one or more purge-gas outlet apertures; one or more purge-gas inlet conduits connected to the pressurizable vessel in fluid communication with the purge-gas inlet apertures, for introducing a purge gas through the purge-gas inlet apertures; a liquid-sample container for holding a liquid sample inside the pressurizable vessel; and a sample tube extending from beneath the surface of the liquid sample in the container to the analytical instrument.
The methods and apparatuses in accordance with the invention allow for pneumatic transfer of ultra-high-purity liquid-chemical samples in a manner that can effectively prevent contamination during the transfer process.